Family guest musicians
Mal Evans contributed to the handclapping parts, while background vocals were performed by Yoko Ono and Pattie Harrison.
"'Birthday' was written in the studio. Just made up on the spot. I think Paul wanted to write a song like 'Happy Birthday Baby', the old fifties hit. But it was sort of made up in the studio. It was a piece of garbage." - John
"We thought, 'Why not make something up?' So we got a riff going and arranged it around this riff. We said, 'We'll go to there for a few bars, then we'll do this for a few bars.' We added some lyrics, then we got the friends who were there to join in on the chorus. So that is 50-50 John and me, made up on the spot and recorded all on the same evening. I don't recall it being anybody's birthday in particular but it might have been, but the other reason for doing it is that, if you have a song that refers to Christmas or a birthday, it adds to the life of the song, if it's a good song, because people will pull it out on birthday shows, so I think there was a little bit of that at the back of our minds." - Paul
- September 18, 1968 (complete track, overdubs, mono mixing)
- October 14, 1968 (stereo mixing)